1. Field of the Invention
The present invention relates generally to the field of fuel delivery units. More specifically, the present invention is directed to a motor vehicle fuel pump installed in a fuel tank having a preliminary stage and a main stage. The device desirably includes an anti-surge cup provided for filling by the preliminary stage in order to collect fuel for the main stage, which feeds from the anti-surge cup. The preliminary stage and the main stage be driven by a vertical shaft.
2. Description of the Related Art
Fuel delivery units similar to this type are frequently used in today""s motor vehicles and are known from practice. In the case of the known fuel delivery unit, the preliminary stage and the main stage of the fuel pump are in each case configured as peripheral pumps and have impellers fastened on the vertical shaft. The vertical shaft is a motor shaft of an electric motor likewise arranged in the anti-surge cup. The preliminary stage is generally arranged below the main stage and fills the anti-surge cup via an ascending pipe. The main stage sucks in fuel from the anti-surge cup and generates pressure necessary for an internal combustion engine of the motor vehicle. Because of this, the fuel delivery unit turns out to be very compact.
A disadvantage of the known fuel delivery unit is that it is of a very large size and that the impellers of the delivery pump are arranged very high up in the fuel delivery unit. As a result, a very high fuel level is required in each case in the fuel tank and in the anti-surge cup for the fuel delivery unit to be able to deliver fuel. When there is a very high level in the fuel tank, there is also the risk, particularly when the fuel tank is going round a corner or when the fuel is hot, of the preliminary stage sucking in air or fuel vapors and producing foam with the fuel and delivering the foam into the anti-surge cup.
The invention is based on the problem of designing a fuel delivery unit of the type mentioned at the beginning in such a manner that it is constructed in a particularly compact manner, and that the impellers of the delivery pump are arranged as low down as possible.
According to the invention, this problem is solved by the preliminary stage having an outlet channel which points radially outward and rises upward. By means of this design, gas bubbles present in the preliminary stage can be guided away via its outlet channel in a very simple manner. Outside the delivery pump the outlet channel can be deflected into the perpendicular ascending pipe of the known fuel delivery unit. Because the outlet channel rises upward, a column of liquid present in the ascending pipe cannot adversely affect the escape of the gas bubbles. Since the outlet channel of the preliminary stage is guided radially, the impellers of the preliminary stage and of the main stage can be arranged very close together and can be mutually arranged very close to the bottom region of the fuel tank. As a result, a particularly low level is required in the fuel tank in order to operate the fuel delivery unit according to the invention. The fuel delivery unit according to the invention additionally turns out to be particularly compact.
A contribution is made to further reducing the dimensions of the fuel delivery unit according to the invention if the main stage has a vertical inlet channel leading from a delivery chamber of the main stage as far as the bottom region of the anti-surge cup. A further advantage of this design is the fact that the delivery pump has, apart from the deflection at the ascending pipe, straight inlet channels and outlet channels. As a result, the risk of hot fuel evaporating is kept particularly small.
According to another advantageous development of the invention, the delivery pump is constructed in a structurally simple manner if the outlet channel of the preliminary stage widens continuously from the delivery chamber of said preliminary stage. The preliminary stage could be configured, for example, as a peripheral pump having blade chambers arranged in the periphery of the impeller. However, this requires the impeller to be set precisely to the delivery pump""s axial clearance. According to another advantageous development of the invention, this type of setting can be avoided in a simple manner if the preliminary stage is designed as a side channel pump, and the delivery chamber is arranged exclusively in one of its end sides. As a result, different pressures prevail on the end sides of the impeller of the preliminary stage, so that the impeller is pressed to the side having the lower pressure. This effect is additionally assisted by leakage of fuel overflowing from the main stage on the shaft to the preliminary stage.
According to another advantageous development of the invention, the delivery pump can be manufactured particularly cost-effectively if the impeller of the preliminary stage, together with a housing part of the fuel pump, which housing part is part of a delivery chamber, is configured as an axial bearing for the fuel pump. It is preferred that an electric motor be used for driving the fuel pump. In order to form the axial bearing, the impeller and the housing part may, for example, have a slidable coating or pockets for producing a sliding film from fuel.
Fuel flowing back into the fuel tank from the internal combustion engine of the motor vehicle is generally fed to the anti-surge cup. According to another advantageous development of the invention, the fuel is prevented from heating up in the preliminary stage if a housing wall between the preliminary stage and the main stage is manufactured from a thermal-insulating material. By this means, the risk of evaporation of the fuel in the inlet channel of the preliminary stage is kept particularly small.
According to another advantageous development of the invention, a contribution to further reducing the transfer of heat from the main stage to the preliminary stage is made if blade chambers of the preliminary stage are arranged on that end side which faces away from the main stage. According to another advantageous development of the invention, fuel sucked in from the preliminary stage can be particularly reliably prevented from swirling if the anti-surge cup has a recess in the center of its bottom region for sucking-in fuel by the preliminary stage, and if an inlet channel of the preliminary stage is arranged running vertically toward the impeller of the preliminary stage. As a result, the fuel delivery unit according to the invention furthermore turns out to be particularly compact. The delivery unit according to the invention can also be produced and fitted in a simple manner.